Marketo's implementation of Velocity imports everything as a string, not as an integer as you'd expect. Strings all the way down, right?

Right, fields on leads/contacts will be serialized as a string, with sometimes cumbersome results. Calling toInteger to get a real Integer isn't the worst of it, the way you have to match Booleans ("1" or "") and Dates (all the timezone stuff I was always write) is more annoying.

Fields on custom objects can be native Integers and Doubles. Still no Booleans or Dates, though.